1. Field of the Invention
The invention relates to an improved planisphere of the type disclosed in U.S. Pat. No. 3,858,334, which planisphere is directly programmable to provide local hour angle for entry into published sight reduction tables for navigational purposes. Time zone indications to facilitate correct programming of the planisphere and means for directly obtaining declination information for stars are also provided by the improved planisphere. In addition, the improved planisphere includes unique transit scale indicator structure providing full visualization of the planisphere dial scales.
2. Description of the Prior Art
In the past, instruments such as H.O. 2102-D referred to in more detail in U.S. Pat. No. 3,858,334 have been utilized for navigational purposes and particularly to determine initial line of sight from an estimated position toward a heavenly body for navigational purposes. H.O. 2102-D is deficient, however, in that the steps required are not in accordance with the actual movement and placement of the various elements involved in determining an initial line of sight; that is, the heavenly bodies, the Earth, and an assumed navigator position.
Thus, in using H.O. 2102-D, star distances are initially measured in astronomical terms. While no apparent error of application is involved with positioning the stars according to easterly right ascension, such positioning of the stars is unfortunate since the whole procedural design of direction and all of the pertaining elements developed for celestial navigation are all otherwise on a westerly direction course.
Accordingly, H.O. 2102-D is not generally understood and is used less than a more nearly conceptually correct instrument would be.
A better approach is to consider the same distribution of star positions on a westerly basis in terms of sidereal hour angle as in the present invention. As an added benefit from this better approach to the star locations, it is possible to effect a combination that allows proper diagram type programming of the present invention. With the present invention, the required elements are exactly in strict conformance with the same elements employed in the universal application of navigation diagrams and are useful in providing computed answers for the navigator's work sheet in the determination of the Sumner Line of Position by the Marcq St. Hilare Method of celestial navigation. The 2102-D starfinder and identifier does not work in such a straightforward way.
The present invention also incorporates right ascension scales. However, their employment is only intended to be used as a basis of providing astronomical considerations to those who may wish to use them in connection with applications where astronomical telescopes are employed. Such uses of the invention are aside from the main purpose of the present invention which is to adhere primarily to basic celestial navigation requirement restricted to sidereal hour angle or westerly scales of measure.
While the structure disclosed in U.S. Pat. No. 3,858,334 presents the elements represented therein in their proper relation, in order to provide direct entry into the sight reduction tables H.O. Publication No. 229 of the United States Naval Oceanographic Office, for marine navigation, the local hour angle of a heavenly body is required.
Further, U.S. Pat. No. 3,858,334 does not have time zone indications thereon or means for determining the declination of heavenly bodies in conjunction with the reference indicator thereof.
Also, the transit scale indicator of the structure of U.S. Pat. No. 3,858,334 completely covers some small portion of the dial scales on both sides of the planisphere so that some information on the planisphere is obscured on both sides of the planisphere at all times.